Air conditioning economizer control method and apparatus

ABSTRACT

An air conditioning economizer control method and apparatus for integrating the operation of the economizer with an air conditioning system is disclosed. An economizer position control arrangement is further disclosed incorporating a rotor locking circuit for maintaining the damper in position against a bias applied by mechanical means such as a spring. A multiple position indicator or multiple temperature sensor is utilized to modulate the position of the damper utilizing the motor for opening the damper, a spring for returning the damper and a rotor locking circuit for maintaining the damper in position. Multiple temperature sensors are also disclosed for making effective use of outdoor air when cooling through economizer operation is available. Staged cooling loads relative to outdoor ambient temperatures are utilized to select the appropriate mode of operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to air conditioning apparatus and a methodof control. More particularly, the present invention concernsintegration of an economizer with the operation of an air conditioningunit including means for modulating the damper regulating air flowthrough the economizer.

2. Description of the Prior Art

A typical air conditioning system having a vapor compressionrefrigeration circuit includes various components such as a compressor,condenser, evaporator and expansion device. These components arearranged to transfer heat energy between a fluid in heat transferrelation with the evaporator and a fluid in heat transfer relation witha condenser. To provide cooling to an enclosure heat energy is rejectedin an outdoor coil serving as a condenser and heat energy is absorbed atthe indoor coil serving as an evaporator. This heat energy is absorbedfrom the air being supplied to the enclosure such that air at a reducedtemperature is provided.

It is known in the air conditioning industry to provide an airconditioning unit which is suitable for being mounted on a roof orotherwise adjacent to the enclosure to be conditioned. This unit istypically divided into an indoor section having an indoor heat exchangerand an outdoor section having an outdoor heat exchanger. An indoor fanis mounted within the indoor section for supplying conditioned air tothe enclosure. The indoor fan draws this air both from the enclosure asreturn air and from the ambient as makeup air. The air entering theindoor section is passed in a heat exchange relation with the indoorheat exchanger wherein either heat energy is absorbed from the airflowing therethrough or heat energy is rejected to said air.Consequently the air being supplied to the enclosure is conditionedwithin the indoor section of the air conditioning unit.

The outdoor section of the unit is arranged such that heat energy may betransferred between the outdoor heat exchanger and the ambient airflowing therethrough. Typically, an outdoor fan is provided to circulatethe air through the outdoor heat exchanger. The compressors of a typicalsystem are located within the outdoor section.

It has been found advantageous to utilize air conditioning systemsincorporating economizers. As used herein, the term economizer shallrefer to that portion of an air conditioning unit adapted to drawambient air into the indoor section of the unit for supply to theenclosure. It is desirable to circulate outdoor air to the enclosurewhen its temperature and humidity is such that cooling of the enclosuremay be accomplished without operating the refrigeration circuit of theair conditioning unit or may be accomplished utilizing cool ambient airand simultaneously operating the refrigerant circuit.

Utilization of an economizer requires that sufficient volumes of air becirculated such that air may be drawn into the unit through theeconomizer and thereafter circulated to the enclosure. A sufficientvolume of return air must also be circulated back to the airconditioning unit from the enclosure. Under some conditions, a powerexhaust fan, return air fan or discharge opening may be utilized suchthat the return air from the enclosure is discharged to the ambient.Hence, any cooling effected in this mode of operation is caused by thesubstitution of cool outdoor ambient air for the existing indoor air.The temperature of the outdoor air, as compared to the temperature ofthe enclosure, is typically the critical factor involved in determiningwhether it is more cost effective to effect cooling by circulation ofambient air into the enclosure as opposed to operation of therefrigeration circuit.

The invention as disclosed herein concerns controls for integrating theoperation of an economizer and vapor compression refrigeration circuitfor supplying cool air to an enclosure in the most cost effectivemanner. The control circuit further concerns the incorporation ofcircuits to modulate dampers to provide the correct amount of outdoorair to maintain the appropriate return air temperature to the enclosure.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an air conditioningsystem utilizing outdoor ambient air.

It is a further object of the present invention to provide a controlsystem for incorporating economizer operation with a vapor compressionrefrigeration circuit for effectively supplying cool air to anenclosure.

It is another object of the present invention to provide an apparatusand method for modulating the position of damper blades in aneconomizer.

It is a further object of the present invention to provide a safe,economical and reliable control system for regulating the operation ofan air conditioning system.

These and other objects will be apparent from the description to followand from the appended claims.

These objects are achieved according to the preferred embodiment of thepresent invention by the utilization of a control circuit forintegrating economizer operation with the operation of the compressor ofan air conditioning system to effect cooling of an enclosure. The airconditioning system includes a two stage indoor thermostat for sensingboth a first stage cooling load and a second stage cooling load. Asecond ambient thermostat is provided to close at a second threshholdtemperature and a first ambient thermostat is provided to open at afirst lower threshhold temperature. A first circuit is provided forenergizing the economizer to allow ambient air to enter the enclosurewhen the ambient air temperature is below the first threshholdtemperature upon a first stage cooling load being detected. A secondcircuit means for energizing the economizer upon the ambient airtemperature being above the first threshhold temperature and below thesecond threshhold temperature upon a first stage cooling load beingdetected and for energizing the compressor simultaneously with theeconomizer upon a second stage cooling load being detected is provided.A third circuit means acts to energize the compressor upon a first stagecooling load being detected and the ambient temperature exceeding thesecond threshhold temperature. An additional compressor may be energizedwhen the control circuit detects a second stage cooling need and theambient temperature exceeds the second threshhold level.

An economizer control for regulating the flow of ambient air into thespace to be conditioned includes means for defining an air flow path,damper means for controlling the air flow therethrough, spring means forbiasing the damper towards the closed position, motor means for biasingthe damper towards the open position and motor locking means forelectrically locking the motor means in position to maintain this damperin position notwithstanding the spring means. Both switches fordetermining a vent position and sensing means for determining operatingpositions are provided for appropriately energizing either the motormeans or the motor locking means to maintain the damper in theappropriate position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic wiring diagram of an air conditioning unitincorporating an economizer control.

FIG. 2 is a plan type view of a rooftop type air conditioning unitdisclosing an economizer and damper arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment herein will be described with particularreference to a unitary rooftop type air conditioning unit. It is to beunderstood that the application of this economizer and damper controlscheme is not limited to this particular type of air conditioningequipment or to an application of the exact nature as described. It isfurther to be understood that although specific switching and sensingparameters are disclosed other equivalent parameters or means may beutilized for accomplishing the same functions.

Referring first to FIG. 2, there may be seen a rooftop type airconditioning unit 10 divided by partition 12 into indoor section 20 andoutdoor section 30,. Outdoor section 30 includes outdoor heat exchanger32, compressors 35 and 36 and outdoor fan 34 powered by outdoor fanmotor 33. Indoor section 20 includes indoor heat exchanger 22, indoorfan 24 powered by indoor fan motor 25 and mixed air thermostat 27 havingmixed air capillary 26 for sensing the temperature of the air enteringthe indoor heat exchanger.

Economizer section 40 is shown having compressor lockout switch 41 andoutdoor ambient temperature sensor 42 located to sense the temperatureof the ambient air. Economizer damper 43 is shown for regulating airflow into the unit through economizer opening 45. Return damper 28 isshown for regulating return air flow to the unit. Motor 29 is connectedto both return damper 28 and economizer damper 43 for simultaneouslyregulating the position of each damper. A spring located within motor 29is connected to bias the dampers such that the return air damper ismaintained in the open position and the economizer damper is maintainedin the closed position.

Air flow into and about the indoor section of the unit is shown byarrows. Return air is supplied from the bottom of the unit upwardly andambient air is supplied from the side of the unit through the economizersection. These two air flow streams mix in the area where the airtemperature is sensed by the mixed air thermostat capillary 26 and thenthe air flows through the indoor coil into indoor fan 24. From the fanthe air is discharged downwardly and returned to the enclosure throughthe bottom of the unit and indicated to be the supply air flow. Heatingmeans may additionally be provided for supplying heat energy to thesupply air. This unit is described as a heat pump capable of reversecycle operation for heating the air supplied to the enclosure.Additional heating means would be supplemental heaters in a unit whichserves as a heat pump or the primary heating means in a unit that doesnot have reverse cycle capabilities.

Referring now to FIG. 1 there may be seen a wiring schematic for thisunit. Power is supplied to the unit at lines L-1 and L-2. Line L-1,designated as wire 101, is connected to normally open first compressorrelay contacts C1-1 and second compressor or relay contacts C2-2, indoorfan relay contacts IFC-1, reversing valve relay contacts RVR-1, heatingcontactor contacts HC-1 and the primary winding of transformer T-1. LineL-2, designated as wire 102 is connected to first compressor motorCOMP-1, second compressor motor COMP-2, outdoor fan motor OFM and indoorfan motor IFM, reversing valve solenoid RVS, to the electric heaters andto the primary winding of transformer T-2. Wire 103 connects firstcompressor relay contacts C1-1 with first compressor motor COMP-1 andoutdoor fan motor OFM. Wire 104 connects second compressor relaycontacts C2-1 with second compressor motor COMP-2.

Wire 105 connects normally open indoor fan relay contacts IFC-1 withindoor fan motor 25 and with the primary transformer T-2. Wire 107connects heating contactor contacts HC-1 with the electric heaters.

A thermostat portion of the diagram, that portion within the dottedlines labelled as thermostat 50, includes numerous temperature sensingdevices. Specifically, power is supplied to wire 110 connected to thesecondary winding of transformer T-1 and to multiple portions of modeswitch 52. Mode switch 52 has cool, auto, heat and off positions forselecting the mode in which the unit is to be operated. Wire 110 isconnected to the power side of the mode switch and is connected to fanswitch FS and normally open reversing valve relay contacts RVR-2. Theupper portion of mode switch 52 has the cool and auto positionsconnected by wire 114 to the first stage cooling thermostat TC-1 and tosecond stage cooling thermostat TC-2. Wire 116 connects the auto andheat portions of the bottom half of mode switch 52 to the first stageheating thermostat TH-1 and the second stage heating thermostat TH-2.

First stage cooling thermostat TC-1 is connected by wire 118 to fanswitch FS. Fan switch FS is connected by wire 132 to second damper relaynormally closed contacts DR2-3 and second damper relay normally opencontacts DR2-4 of the economizer control portion 60 of this wiringdiagram. Wire 122 is connected to the second stage cooling thermostatTC-2 and to compressor lockout switch CLS or 41. Wire 124 connects thefirst stage heating thermostat to reversing valve relay RVR. Wire 126connects the second stage heating thermostat TH-2 to heating contactorrelay HC. Wire 120 connects fan switch FS and indoor fan contactor IFC.Wire 128 connects normally open reversing valve relay contacts RVR-2with normally open reversing valve relay contacts RVR-3, firstcompressor relay C-1, and with normally open second damper relaycontacts DR2-2 and normally closed second damper relay contacts DR2-3.Wire 130 connects normally open reversing valve relay RVR-3 contactswith second compressor relay C-2 and normally closed second damper relaycontacts DR2-1.

Within economizer control portion 60 of the wiring schematic there canbe seen a transformer T-2 connected by wires 105 and 102 such that thetransformer is energized when indoor fan motor 25 is energized. Thesecondary of transformer T-2 is connected to wires 140 and 142. Wire 140is also connected to the outdoor air thermostat OAT (42) to normallyclosed first damper relay contacts DR1-1 and to normally open firstdamper relay contacts DR1-2. Wire 142 is connected to second damperrelay DR2, to motor MTR and to first damper relay DR1. Wire 144 connectsoutdoor ambient thermostat OAT or 42 to normally closed reversing valverelay contacts RVR-4 and wire 145 connects normally closed RVR-4contacts to second damper relay DR2. Wire 146 connects normally closedfirst damper relay contacts DR1-1 to switch SW-1. Wire 148 connectsswitch SW-1 to switch SW-2. Switch SW-1 is connected by wire 156 torotor locking circuit RLC which is connected by wire 158 to motor MTRand to normally closed first damper relay contacts DR1-3 and normallyopen first damper relay contacts DR1-4. Wire 162 connects switch SW-2with normally closed first damper relay contacts DR1-3. Wire 150connects normally open first damper relay contacts DR1-2 with mixed airthermostat first stage MAT-1. Mixed air thermostat first stage MAT-1 isconnected by wire 152 to the second stage MAT-2 of the mixed airthermostat and by wire 154 to wire 156. Wire 160 connects second stageMAT-2 of the mixed air to the normally open first damper relay contactsDR1-4.

Wire 162 connects compressor lockout switch CLS to normally closedsecond damper relay contacts DR2-1 and to normally open second damperrelay contacts DR2-2. Wire 164 connects normally open second damperrelay contacts DR2-4 to the first damper relay DR1.

Spring 90 is shown in a dotted line connection between motor MTR andswitches SW-1 and SW-2. (Spring 90 physically connects the rotor of themotor to the motor frame.) Switches SW-1 and SW-2 are mounted withinmotor MTR which is displaced by spring 90 unless the motor or the rotorlocking circuit is energized. The rotor locking circuit includes a diodeand resistor in series and a capacitor in parallel therewith. Whenenergized the rotor locking circuit prevents the rotor from turningthereby maintaining the damper in the selected position notwithstandingthe bias applied by spring 90.

Operation

In the heating mode of operation, upon a first stage heating need beingsensed, first stage thermostat TH-1 closes and energy is supplied toreversing valve relay RVR. Reversing valve relay contacts close suchthat energy is supplied to the indoor fan contactor IFC and also tofirst compressor contactor C-1 and second compressor contactor C-2. Thevarious compressor contacts being energized act to energize the twocompressors, the outdoor fan motor and reversing valve solenoid.

Upon indoor fan contactor IFC energizing first indoor fan contactorcontacts IFC-1, indoor fan motor 25 is energized and power is suppliedvia wires 102 and 105 to transformer T-2. The secondary of transformerT-2 then supplies power to normally closed first damper relay contactsDR1-1 and to switches SW-1 and SW-2. Switches SW-1 and SW-2 are arrangedto determine the displacement of the damper. At this point, since theunit is in the heating mode of operation, it is anticipated that thedamper will be only open to a vent position to allow the required amountof outdoor air to be mixed with the indoor air. For this vent positionthe two switches are preset to open and close upon a given amount ofdisplacement. The displacement between the switches is spaced slighlysuch that they open and close at different angular displacement. MotorMTR acts to open the damper whereas spring 90, shown by a dotted line,acts to close the damper. Rotor locking circuit RLC, including a diodeand resistor in series and capacitor parallel therewith, acts tomaintain the motor in position against the bias of the spring whenenergized.

Hence, as power is supplied upon startup, switches SW-2 and SW-1 areclosed and power is supplied through wire 162, through normally closedfirst damper relay contacts DR1-3, through wire 158 to the motor. Themotor is then operated until switch SW-2 opens breaking contact. SwitchSW-1 is arranged to remain closed until a small displacement occursafter switch SW-2 opens. In the closed position, switch SW-1 energizesrotor locking circuit RLC maintaining the motor in that position. Whenpower is no longer being supplied directly to the motor through switchSW-2, the rotor locking circuit, if energized, will act to maintain themotor in position. A stall region is provided between the point whereswitch SW-2 opens and switch SW-1 opens, this region being theacceptable limit within which the damper may rotate while still being inthe vent position. Should the damper overshoot while opening, the switchSW-1 will open allowing the dampers to rotate toward the closed positionvia the bias of the spring until switch SW-1 closes energizing the rotorlocking circuit maintaining the dampers in position. Should the dampersmanage to close further, switch SW-2 will close energizing the motor torotate the dampers to a more open position. Hence, this combination ofswitches with the rotor locking circuit and motor acts to maintain thedampers within the stall region as defined by the switch positions.

During heating operation normally closed reversing valve relay contactsRVR-4 open preventing second damper relay DR-2 from being energized.Hence, the dampers will be maintained in the vent position rather thanan economizer position during heating.

Switching now to the cooling mode of operation it may be seen upon afirst stage cooling need being sensed, wire Y1 is energized. The fan isenergized simultaneously therewith acting to supply power to theeconomizer control through transformer T2. Assuming the ambienttemperature is sufficiently high, such as above 80° F., outdoor ambienttemperature thermostat OAT will open and power will not be supplied tosecond damper relay DR2. Power will be supplied through normally closedfirst damper relay contacts DR1-1 to switches SW-1 and SW-2 to maintainthe damper in the vent position when the outdoor ambient temperaturelevel detected is above a second threshhold level as detected by theoutdoor ambient thermostat. The first damper relay is not energizedsince the power being supplied through wire Y1 cannot pass through thenormally open second damper relay DR2-4 contacts to energize firstdamper relay DR1.

Should the temperature be sufficiently low that the outdoor ambientthermostat OAT is closed then the second damper relay will be energizedand the second damper relay contacts DR2-4 will be closed energizingfirst damper relay DR1. Once the first damper relay is energized thanthe normally open first damper relay contacts DR1-2 are closed supplyingpower to mixed air thermostat MAT and the normally closed first damperrelay contacts DR1-1 are opened discontinuing power to the switchcontacts SW-1 and SW-2. Once the first damper relay is energized theeconomizer may no longer be operated in the vent position. In thisposition, with the outdoor ambient thermostat closed, the temperature ofthe outdoor ambient air is such that ambient air may be drawn into theenclosure to provide cooling.

The mixed air thermostat senses the combined temperature of the returnair and the ambient air just prior to that air entering the indoor coilof the air conditioning unit. The mixed air thermostat incorporates twothermal sensing devices, the second stage MAT-2, connected to energizethe damper motor to open the damper and the first stage MAT-1, connectedto energize the rotor locking circuit to maintain the damper inposition. Typically, the lower temperature level may be set at 50° F.and a higher temperature level set at 54° F. Hence, if the temperaturesensed is above 54° F. the both the MAT-1 and MAT-2 contacts will beclosed and consequently power will be supplied through MAT-2 contactsthrough wire 160, through the now closed first damper relay contactsDR1-4 to motor MTR to further open the damper to allow more outdoor airto enter. Once the temperature of the mixed air drops to 54° the secondstage of the mixed air thermostat opens discontinuing further motoroperation and the rotor locking circuit is energized.

Upon a further drop in temperature below the setpoint of the first stageof mixed air thermostat MAT-1, the rotor locking circuit will bede-energized and the spring will act to close the damper. The rotorlocking circuit will be de-energized until the mixed air temperatureincreases to the MAT-1 setpoint. Hence, it can be seen that thiscombination of mixed air thermostat elements acts to create a modulationof the damper element such that the appropriate amount of ambient air isallowed to enter the unit to maintain the temperature of the air in theindoor section of the unit within the appropriate range.

Should a second stage cooling need be sensed by sensing element TC-2closing, power will be supplied through wire 122 or Y-2. This supply ofpower will be entirely ineffective if compressor lockout switch CLS isopen. The compressor lockout switch is designed to close at atemperature level less than the temperature level at which outdoorambient thermostat OAT closes such that compressors are maintainedde-energized if there is cooling available from the outdoor air. If theoutdoor air temperature is above the temperature at which the compressorlockout switch closes, such as 60° F., then power is supplied throughwire 162 to either first compressor relay C1 through normally closedsecond damper relay contacts DR2-1 if the outdoor ambient thermostat isopen or through second damper relay contacts DR2-2 to first compressorrelay C1 if outdoor ambient thermostat OAT is closed energizing thesecond damper relay.

From the above description of the operation of the unit it may be seenthat upon a first stage cooling need being detected, the compressorlockout switch is ineffective. If the outdoor ambient thermostat switchis open then the economizer may only be operated in a vent position. Ifthe outdoor ambient thermostat is closed than a first stage cooling needwill act to energize the economizer with the damper blades modulating.Upon a second stage cooling need being detected, if the compressorlockout switch is open, then only the economizer will be operated. Ifthe compressor lockout switch is closed and the outdoor ambient switchis closed then the economizer is operated in response to a first stagecooling need being detected and the first compressor is operated inresponse to a second stage cooling load. If the outdoor ambientthermostat is open and the compressor lockout switch is closed then thefirst compressor is operated when a first stage cooling need is detectedand the second compressor is operated when a second stage cooling needis detected.

While the above invention has been described with reference to aparticular embodiment thereof it is to be understood that variations andmodifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A control circuit for integrating economizeroperation with operation of a compressor of an air conditioning systemto effect cooling of an enclosure, said air conditioning systemincluding a two stage thermostat for sensing a first stage cooling loadand a second stage cooling load which comprises:a second ambientthermostat set to close at a second threshhold temperature; a firstambient thermostat set to close at a first threshhold temperature lowerthan the second threshhold temperature; first circuit means forenergizing the economizer to allow ambient air to enter the enclosurewhen the ambient air temperature is below the first threshholdtemperature upon a first stage cooling load being detected; secondcircuit means for energizing the economizer upon the ambient airtemperature being above the first threshhold temperature and below thesecond threshhold temperature upon a first stage cooling load beingdetected and for energizing the compressor simultaneously with theeconomizer upon a second stage cooling load being detected; and thirdcircuit means for energizing the compressor upon a first stage coolingload being detected and the ambient temperature exceeding the secondthreshhold temperature.
 2. The apparatus as set forth in claim 1 whereinthe air conditioning system includes a second compressor and the controlcircuit comprises means for energizing the second compressor in responseto a second stage cooling need being detected when the ambienttemperature exceeds the second threshhold level.
 3. The apparatus as setforth in claim 1 wherein the second ambient thermostat is an outdoor airthermostat and further including a second damper relay connected to beenergized when the outdoor air thermostat senses a temperature below thesecond threshhold level and wherein second damper relay contacts areconnected to energize the economizer if the second damper relay isenergized or the compressor if the second damper relay is not energized.4. The apparatus as set forth in claim 3 wherein the first ambientthermostat is a compressor lockout thermostat which opens when theambient temperature is below a first threshhold temperature and which isconnected to the thermostat to prevent a second stage cooling need fromenergizing a compressor if the temperature sensed by the compressorlockout switch is below the first threshhold level.
 5. The apparatus asset forth in claim 4 wherein additional second damper relay contacts arepositioned to connect the compressor lockout thermostat to the secondcompressor if the second damper relay is not energized and to the firstcompressor if the second damper relay is energized.
 6. A method ofcoordinately controlling an economizer combined with an air conditioningsystem having a vapor compression refrigeration circuit including atleast one compressor, a two stage thermostat for determining coolingneeds, at least one outdoor thermostat and an indoor fan for circulatingair to the enclosure to be conditioned which comprises the stepsof:energizing the indoor fan when a first stage cooling need is detectedby the thermostat; energizing the economizer when a first stage coolingneed is detected and the outdoor ambient temperature is below a secondthreshhold temperature; energizing the compressor of the refrigerationcircuit in response to a first stage cooling need when the ambienttemperature is above a second threshhold temperature; and energizing thecompressor of the refrigeration circuit in response to a second stagecooling need when the ambient temperature is above a first threshholdtemperature which is lower than the second threshhold temperature. 7.The method as set forth in claim 6 wherein the refrigeration circuitincludes a second compressor and further comprising the step ofenergizing the second compressor when a second stage cooling need isdetected and when the ambient temperature is above the second threshholdtemperature.
 8. The method as set forth in claim 7 wherein theeconomizer includes an economizer damper and wherein the step ofenergizing the economizer includes displacing the economizer damper toregulate the flow of ambient air into the enclosure.
 9. The method asset forth in claim 8 wherein the step of energizing the economizerincludes displacing the economizer damper to a vent position when theambient temperature exceeds the seccond threshhold temperature.